What Is The Sum Of 1/2 +1/3 + 1/4 ?

[arjay]

University Challenge question tonight:-
What is the sum of one half, one third and one quarter?
Thank you

[Wizzy67]

13/12 or 1 1/12

[Togo]

Common denominator is 12 . 6+4+3= 13x 12ths or 1 and 1/12. decimal 1.0833rec

[Peter Pedant]

O god it is greater than one ....
not that it matters as the winners caned the losers

I thought Bamber thought it was 12/13

[Jennykenny]

I'm definitely with Whizzy - 1 1/12.

[arjay]

Thank you Wizzy 67 and Togo.
I misunderstood the University Challenge question.
It was not algebraic but about resistors connected in parallel.

[jim360]

The reason the answer to the Uni Challenge question is 12/13 and not 13/12 is because the "resistors in parallel" formula is "One over total resistance equals the Sum of (one over individual resistances)".

[jim360]

... so that, having worked out the sum of 1/2, 1/3 and 1/4, you have to turn the answer upside-down to get the actual answer, ie 13/12 becomes 12/13.

[Togo]

Well crikey arjay that move the goalposts. Was a voltage given to calculate current in amps or was the question about the total resistance of parallel resistors in ohms?

[jim360]

It was about total resistance of parallel resistors, yeah. I got it wrong as I rushed in my head and thought 1/4 = 1/6, giving an answer of 12/11 ... whoops.

[Togo]

Then there is conductance resistance. I loved electronics when I was doing it.

[Togo]

If those values were resistance given in ohms. Then the three resistors in parallel would give an overall resistance of .11107 ohms. A parallel circuit of resistors always has a lower resistance than the lowest individual resistor in the circuit.

[jim360]

Well the values of the resistors were 2, 3, and 4 ohms, so the reciprocals were 1/2, 1/3, and 1/4.

[Togo]

Going to bed now my head hurts.

[Togo]

That would be .92308 ohms jim.

[jim360]

Yes, or... 12/13.

[Togo]

Jim the original post made no mention of parallel resistors or the massive fact that the fractions were reciprocals. 2,3 and 4 ohms would have been easy. Also fractions were rarely used in electronics but we got there. Haha.

[guitpic]

Dont you find a common denominator.
Like 2, 3 and 4 will go into 12. So you get the answer in 12ths. 2 into 12 goes 6 = 6/12. 3 into 12 goes 4= 4/12. 4 into 12 goes 3 = 3/12. Then add the 12ths up 6/12+4/12+3/12= 13/12 which is 1 and 1/12.
So the answer is 1 1/12

[Togo]

Errr that is the answer to the question....... But if you read ALL the replies the question had a hidden riddle. ^^^^^

[chrissa1]

I agree with, guitpic. Good old common denominators.

[Peter Pedant]

thx Jim yes it was on resistors in parallel

one time they had relativistic speeds ( one minus v squared over c squared ) which I thought was a bit sporting to have to sork out in real time